# Tag Info

Accepted

### NIntegrate: the order of singular points matters!

Note that {x, x1, x2, x3,..., xn} describes a path in the real or complex domain, and the order matters. So {x, -5, 2, 0, 5}] ...
• 236k

### What can one do with extremely stiff problem in NDSolve?

EDIT #2 My error was useful. It brought me to the conclusion that the difficulties in solving the PDE of the OP are due to the drift term $$\frac{\partial (x u(x,t))}{\partial x}$$ If the drift ...
• 13.1k

• 2,513
Accepted

### To deal with infinity in NDSolve

The singularity at r == 0 is of the type $O(1/\sqrt{r-1})$ and is easily removed with a substitution $r - 1 = u^2$. As for $r = \infty$, ...
• 236k

### NIntegrate and Integrate giving different results for ill-behaved function

TL;DR Use HeavisideTheta's properties before integration. This is my strategy. First the HeavisideTheta gives you the ...
• 6,727

### How to solve second order nonlinear differential equation?

The desired solution can be obtained semi-analytically. ...
• 61.5k
Accepted

### Why do I get "PrincipalValue cannot work with the specified exclusions" when feeding a list to a function?

Interpreting the OP's example as an MWE and not the actual problem, there are three issues: (1) evaluating the integral for a list of test values; (2) the integral and error being zero; and (3) the ...
• 236k
Accepted

### Numerical integration giving trouble

The integral you are calculating is not a function of $\theta_j$, $\phi_j$. Itâ€™s a constant. In order to see this, note that each pair of angles $(\theta,\phi)$ identifies a point on the surface of a ...
• 978
Accepted

If: ...
• 66.2k